There is currently little information regarding the specific nutritional requirements of HIV-infected infants & children. Failure-to-thrive is commonly reported finding in HIV-infected children and has been associated with a significantly shorter survival time. Poor growth is frequently a presenting symptom if HIV infection, and may be predictive of disease progression. Identification & treatment of nutritional deficiencies may allow patients to remain asymptomatic or mildly symptomatic for a longer period of time. In order to define a strategy for the successtul nutritional maintenance & rehabilitation of HIV- infected children, we propose to identify the early changes which occur in protein & energy metabolism in HIV-infected children. The aim of this proposal is to quantify the nutritional & metabolic changes which occur in HIV-infected children with & without poor growth, and to compare them with age matched HIV-uninfected controls.